Synthesis of a potassium capped terminal cobalt–oxido complex

An unusual example of a potassium capped terminal cobalt–oxido complex has been isolated and crystallographically characterized. The synthesis of [tBu,TolDHP]CoOK proceeds from a previously reported parent compound, [tBu,TolDHP]CoOH, via deprotonation with KOtBu. Structural and electronic characterization suggest a weakly coupled dimer in a distinct seesaw geometry with a Co(iii) oxidation state and a non-innocent radical ligand.


General Methods
All chemicals were purchased from commercial suppliers and used without further purification.All manipulations were carried out under an atmosphere of N2 using standard Schlenk and glovebox techniques.Glassware was dried at 180 °C for a minimum of two hours and cooled under vacuum prior to use.Solvents were dried on a solvent purification system from Pure Process Technologies and stored over 4 Å molecular sieves under N2.Tetrahydrofuran (THF) was stirred over NaK alloy and run through an additional alumina column prior to use to ensure dryness.Solvents were tested for H2O and O2 using a standard solution of sodium-benzophenone ketyl radical anion.CD3CN, C6D6, and d8-toluene were dried over 4 Å molecular sieves under N2. 1 H NMR spectra were recorded on Bruker DRX 400 or 500 spectrometers.Chemical shifts are reported in ppm units referenced to residual solvent resonances for 1 H NMR spectra.UV-visible spectra were recorded on a Bruker Evolution 300 spectrometer and analyzed using VisionPro software.A standard 1 cm quartz cuvette with an airtight screw cap with a puncturable Teflon seal was used for all measurements.A Unisoku CoolSpek cryostat was used for low temperature measurements.IR spectra were recorded on a Bruker Tensor II spectrometer with the OPUS software suite as DCM thin films between KBr plates.Single crystal X-ray diffraction data were collected in-house using Bruker D8 Venture diffractometer equipped with Mo microfocus X-ray tube (λ = 0.71073 Å).Electrochemical measurements were carried out using a BAS Epsilon potentiostat and using BAS Epsilon software version 1.40.67 NT.EPR spectra were recorded on an Elexsys E500 spectrometer with an Oxford ESR 900 X-band cryostat and a Bruker Cold-Edge Stinger and were simulated using the Easyspin suite in Matlab software. 1Magnetic moments were determined using the Evans method. 2 Synthesis of [ tBu,Tol DHP]CoOK (1)   In a 20 mL vial in the glovebox, 2 mL of toluene was added to [ tBu, Tol DHP]CoOH (0.002 g, 1 eq., 0.004 mmol). 3A suspension of potassium tert-butoxide (0.0022 g, 5 eq., 0.020 mmol) in toluene was added to the bright purple solution of [ tBu, Tol DHP]CoOH.After stirring for 1-2 h, or until the suspended white solids were no longer visible, the resulting green-purple solution was dried in vacuo and extracted into benzene.Complex 1 can then be isolated as a purple solid after crystallizations in petroleum ether.Yield: 0.0019 g, 88 %.Poor quality single crystals suitable for XRD of 1 were grown out of a cooled concentrated petroleum ether solution at -35 o C. 1 H NMR (400 MHz, C6D6, RT): δ = 10.92 (br s), 8.44 (s), 6.67 (s), 1.88(s), 1.50(s).Magnetic Susceptibility: Evans' Method for 1 (C7D8 RT, 500 MHz, µB): µeff = 3.62, UV-vis, nm in toluene, (ε, M −1 cm −1 ): 2213.32.HRMS (EI) m/z: [M] + calculated for 1: C28H34N5OKCo 554.1732 found: 554.1775.
In practice, this compound can also be obtained from [ tBu, Tol DHP]CoCl or OTf via addition of wet KO t Bu. 4

Preparation of UV-Vis Samples
An aliquot of complex 1 was dissolved in toluene in a quartz cuvette in the glove box.The 1 cm quartz cuvette was equipped with an airtight screw cap.The spectrum was collected under a blanketing flow of Nitrogen.

Preparation of IR Samples of (1)
Separate samples of complex 1 and [ tBu, Tol DHP]CoOH were dissolved in dry dichloromethane to form a concentrated solution.This was dropcast onto a KBr plate, and a second plate was then placed on top.The sample was then transferred in an air-free temporary container to the spectrometer, and a spectrum was collected.

Electrochemical Experiments
Experiments were performed inside the glovebox with a 1:4 MeCN:THF 0.1 M KPF6 electrolyte solution at room temperature.Cyclic voltammetry measurements were made with a [Co] = 2.4 mM using a glassy carbon working electrode, platinum wire counter electrode, and silver wire pseudo reference electrode and were referenced to internal Fc/Fc+ by adding ferrocene at the end of measurements.A one-compartment glass cell was filled with 4 mL of electrolyte solution.The working electrode was polished over a microcloth pad (Buehler) using alumina slurry (0.05mm EMS), followed by rinsing with deionized water and isopropyl alcohol.Reference and counter electrodes were rinsed with acetone.CVs were recorded at a scan rate of 200 mV/s scanning oxidatively.

Density Functional Theory (DFT) Geometry Optimizations
Geometry optimization calculations and single point energy calculations were performed with ORCA 6 software suite using density functional theory (DFT).Geometries were fully optimized starting from coordinates generated from finalized cifs of the compound crystal structures when possible.The O3LYP functional was used for geometry optimizations, spin density plot calculations, and single point energy calculations.For the O3LYP calculations, def2-TZVPP was used on Co, N, S, O, and F, and def2-TZVP on C and H atoms.A CPCM solvation model for benzene was used throughout.Due to the challenge of simulating the dimeric OK complex, the calculation energies here do not include entropic contributions.Table S3.SXRD of [

Figure
Figure S15.IR comparing IR of 1 (purple) as a thin film to IR of [ tBu, Tol DHP]CoOH (blue) as a thin film.The OH peak of [tBu, TolDHP]CoOH is marked by an asterisk (*) and is generally consistent DFT calculated values.3However, we note a few overlapping stretches, presumably from C-Hs.The low frequency of this OH made arise from hydrogen bonding interactions between molecules.

Figure S22. Calculated structure of 1 .
Figure S22.Calculated structure of 1.All C-H hydrogen atoms have been removed for clarity

Table S4 .
Simulated g-values for EPR of 1

Table S5 .
Single Point Energy Calculations of 1 with the addition of different acids

Table S6 .
Single Point Energy Calculations of 1 with different alkali metal cations

Table S7 .
pKa values for acids used in pKa bracket study